In a typical communications network, a wireless device communicates via a Radio Access Network (RAN) to one or more Core Networks (CNs). The communications network may also be referred to as e.g. a wireless communications network, a wireless communications system, a communications network, a communications system, a network or a system.
The wireless device may be a device by which a subscriber may access services offered by an operator's network and services outside operator's network to which the operator's radio access network and core network provide access, e.g. access to the Internet. The wireless device may be any device, mobile or stationary, enabled to communicate over a radio channel in the communications network, for instance but not limited to e.g. user equipment, mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The wireless device may be portable, pocket storable, hand held, computer comprised, or vehicle mounted devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another wireless device or a server.
The wireless device is enabled to communicate wirelessly within the communications network. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone, between the wireless device and a network node, between network nodes, and/or between the wireless device and a server via the radio access network and possibly one or more core networks and possibly the Internet.
The communications network may cover a geographical area which may be divided into cell areas. Each cell area is served by a base station. The base station may be referred to as a Radio Base Station (RBS), evolved Node B (eNB), eNodeB, NodeB, B node, or Base Transceiver Station (BTS), depending on the technology and terminology used.
A radio communication between a wireless device and a base station may be affected by multi path propagation, fading, frequency errors, round trip times etc. The communication channel between the base station and the wireless device may be referred to as an air interface, and may cause bit and block errors on information transmitted using the communication channel. A receiver may be designed in order to reduce bit error and block error rates which, among others, comprise channel estimation, antenna combining, equalization and demodulation. An accurate channel estimate may be crucial for equalization and thus also for demodulation and decoding of the user data.
The wireless device may change the amplitude of an uplink transmitted signal depending on TPC commands, which are received in downlink from a base station. Furthermore, the received signal may also be scaled by an AGC by the base station. The channel estimate should thus vary according to both the fading radio channel and these changes in amplitude due to TPC commands in the wireless device and the AGC in the base station. The wireless device may be seen as a transmitter and the base station may be seen as a receiver. Uplink may be defined as the direction from the wireless device to the base station, and downlink may be defined as the direction from the base station to the wireless device.
In e.g. a Wideband Code Division Multiple Access (WCDMA) network one key component is to maintain a received Signal to Interference plus Noise Ratio (SINR) at a constant level to preserve the quality of the received information at a desired level. SINR is a measure of signal strength relative to background noise and interference. The base station receives a signal from the wireless device and measures the SINR of the received signal, and then the measured SINR value is compared with a SINR threshold-value to generate a TPC command. The TPC command is sent to the wireless device and indicates to the wireless device whether it should increase or decrease its transmitting power. The wireless device adjusts its transmitting power based on the received TPC command. The adjustment may take place for example once for a time slot. A time slot, also referred to as slot, may be described as being a kind of a time interval, a time assigned on a schedule, an allocated period of time etc. A time slot may be transmitted in either the uplink or downlink direction. In some embodiments, time slots may be dynamically assigned in order to provide variable and asymmetrical data transmission rates. Using WCDMA as an example, where both uplink and downlink data channels are segmented into time slots and frames. Such slot may be e.g. 666.667 psec in length, and fifteen of these time slots are concatenated to form a 10 millisecond (ms) frame. Using LTE as an example, a frame and slots may be of various lengths. For example, a frame may have an overall length of 10 ms and this is then divided into 20 individual slots.
If the wireless device moves towards the base station, the signal strength increases and causes an increased interference level as seen by other wireless devices. In this case, the base station needs to send an instruction to the wireless device to reduce its transmission power as it moves towards the base station. If the wireless device moves away from the base station it may suffer from increased path loss. In this case, the base station needs to send an instruction to the wireless device to increase its transmission power as it moves away from the base station.
According to some embodiments of the Third Generation Partnership Project (3GPP), the wireless device's transmission power may be updated each 0.667 ms based on a signal quality measurement done in the base station. 3GPP describes two different inner loop power control algorithms. In the inner loop power control, the base station sends an UpLink (UL) TPC command to the wireless device comprising instructions to increase or decrease its transmission power. The wireless device adjusts its transmission power according to the TPC command and sends a signal according to the adjusted transmission (Tx) power, back to the base station.
A description of TPC scaling within the wireless device in uplink for WCDMA is given in section 5.1.2.2 of 3GPP TS 25.214, V.11.5.0. In 3GPP TS 25.214, V.11.5.0 two alternative algorithms, algorithms 1 and 2, are supported in the wireless device of how to derive the TPC scaling. The selection of which algorithm to use is specific for the wireless device, and the selection is specified by the network. The TPC scaling is denoted by ΔDPCCH in the following description.
For “Algorithm 1”:
                If the received TPC command is equal to 1, then ΔDPCCH=+1 dB or +2 dB for that slot.        If the received TPC command is equal to 0, then ΔDPCCH=−1 dB or −2 dB for that slot.+ indicates that the wireless should increase the power and − indicates that the wireless device should reduce the power.For “algorithm 2”:        For the first four slots of a set, then ΔDPCCH=0 dB.        For the fifth slot of a set, the wireless device uses hard decisions on each of the five received TPC commands as follows:                    If all five hard decisions within a set are 1 then ΔDPCCH=+1 dB in the 5th slot.            If all 5 hard decisions within a set are 0 then ΔDPCCH=−1 dB in the 5th slot.            Otherwise, ΔDPCCH=0 dB in the 5th slot.                        
A hard decision of a TPC command is a binary decision of either “1” or “0” without any information of the probability, quality measure or other judgment of this decision. TPC steps inside the channel estimation may be compensated for. Compensation for TPC steps inside the channel estimation was suggested in WO 2012/118415. In WO 2012/118415, the knowledge of TPC is achieved by assuming that the wireless device is not in handover and that the time delay of the TPC commands can be estimated.
The term handover mentioned above may be described as the process of transferring an ongoing call or data session from one channel connected to the core network to another. The term channel estimation mentioned above, may be performed by a channel estimator and may be described as to estimation of the frequency response of the path between the transmitter and receiver. The channel estimation may be used to optimize performance and maximize the transmission rate.
The wireless device may change the amplitude of the uplink transmitted signal depending on at least one TPC command. As mentioned above, these TPC commands are determined by the base station and transmitted on the downlink from the base station to the wireless device. However, the wireless device might simultaneously receive TPC commands from several base stations. In this case, the base station does not know if the wireless device is acting according to its transmitted TPC commands. A scenario in which a wireless device receives multiple TPC commands from several base stations is in handover between base stations. Thus, the processing with the receiver of the base station cannot rely upon that the wireless device follows the TPC commands which it transmits. Furthermore, the delay between transmitting the TPC commands in downlink until the wireless device uses the TPC command in the uplink is unknown.
AGC, which is an acronym for Automatic Gain Control or Automatic Gain Controller, may be found in any device or system where wide amplitude variations in the input signal may lead to a loss of information or to an unacceptable performance of the device or the system. This way, saturation of various circuit blocks in the device or system may be avoided. The role of the AGC is to automatically adjust the gain of an input signal in order to provide a relatively constant output amplitude. This means that units following the AGC require a smaller dynamic range. The AGC may also be described as an adaptive system where the average output signal level is fed back to adjust the gain to an appropriate level for a range of input signal levels. For example, without the AGC the sound emitted from an Amplitude Modulation (AM) radio receiver would vary to an extreme extent from a weak to a strong signal. The AGC effectively reduces the volume if the signal is strong and raises it when it is weaker.
The base station might be equipped by an AGC. This AGC scales the received signal such that the dynamic range of the signal is lowered. A low dynamic range is beneficial in order to reduce quantization errors and errors due to truncation of large values. Typically, this AGC scaling is only allowed to change at predefined time instants. Also, the amplitude and the time of the AGC scaling are known by the base station. Nevertheless, the scaling impacts the amplitude of the signals used in the channel estimator and in the equalizer.
A channel estimator typically tries to estimate the radio channel between the wireless device and the base station in the sense that the channel estimates follows both radio channel fading as well as TPC and AGC steps. Due to the inherit linear filtering in the channel estimator, the TPC steps and changes in AGC scaling will be smoothed into slowly time varying channel estimates, as illustrated in FIG. 1. FIG. 1 illustrates a true channel, i.e. an ideal channel estimate, and a channel estimation without TPC or AGC compensation. The x-axis in FIG. 1 represent slots number 115-130. The y-axis in FIG. 1 represents the real value of the channel at base station antenna 0. The crossed line in FIG. 1 represents real values of an ideal channel estimate. The circled line in FIG. 1 represents real values of a tracker channel estimator. In the illustration in FIG. 1, the TPC scalings are seen in changes of the amplitude by 1 dB between all slots. Changes in the AGC scaling may occur anywhere within a slot, but in this illustration the changes in AGC scaling also occurs between slots, see e.g. the change between slot 120 and 121 in FIG. 1. However, the changes in the AGC scaling typically occur at a lower rate than the amplitude changes due to the TPC scaling.
An illustration is given in FIG. 2 of a true channel, i.e. ideal channel estimate, and a channel estimate in which the received signal is compensated with TPC and AGC scaling before the processing in the channel estimator, such that the channel estimator has an input signal without amplitude changes due to the TPC scaling and changes in AGC scaling. The x-axis in FIG. 2 represent slots number 115-130. The y-axis in FIG. 2 represents the real value of the channel at base station antenna 0. The crossed line in FIG. 2 represents real values of an ideal channel estimate. The circled line in FIG. 2 represents real values from a tracker channel estimator when the received signal is compensated with TPC and AGC scalings. After the channel estimation, the amplitude steps of the signal due to the TPC scaling and changes in the AGC scaling are applied again to the estimated channel
A channel estimates will deviate from the true the channel if the impact of the TPC scaling and the AGC scaling is not considered within the channel estimation, resulting in bit and block errors on the uplink communication link.